1. Field of the Invention
This invention relates to a light emitting device and a light emitting apparatus.
2. Background Art
Light emitting elements such as LEDs (Light Emitting Diodes) provide highly energy-efficient light sources and are widely used in illumination and display devices to replace incandescent lightbulbs for energy conservation and the like. In recent years, devices emitting white light with high luminous flux are drawing attention as replacements for fluorescent tubes.
A semiconductor light emitting element used in an LED generally emits light in a designated wavelength region such as blue, green, or red. Therefore, the light produced by a light emitting element can be used to emit light having a white or intermediate color by performing wavelength conversions by fluorescent materials. In other words, multiple types of fluorescent materials which emit light in designated wavelength regions such as blue, green, yellow, and red can be used to emit light having a white or intermediate color.
In such a case, known methods dispose adjacent fluorescent material layers that emit light of different wavelengths, and known structures have stacked fluorescent material layers with light transmitting layers therebetween. However, when using such methods providing multiple layers, luminous flux is low due to reflections of light at interfaces between layers and light refraction between layers having different refractive indexes. Moreover, although it is generally necessary to disperse an inorganic granular fluorescent material in a transparent material such as epoxy resin or silicone resin to form multiple layers including fluorescent materials by such methods, control of the dispersion state is difficult, and manufacturing processes become undesirably complex.
Therefore, one proposed configuration covers an LED with fluorescent glass having fluorescent material grains mixed therein to emit red, green, and blue light (JP 3978102). However, no consideration is given to the absorptance of the fluorescent glass and the fluorescent material grains. Therefore, there is room for improvement in regard to conversion efficiency.